All N:NIH(S)-B mice have multiple foci of hepatic necrosis and inflammation. The cause of hepatitis is unknown. This mouse strain was developed at the NIH Genetic Resource for use as foster mothers in a barrier facility. The mice appear clinically normal, but have macroscopic, microscopic, and biochemical liver abnormalities. Studies were conducted to determine the etiology of hepatitis, to rule out the presence of an infectious agent, and to explore the pathogenesis of hepatitis in this strain. High levels of dietary vitamin A was examined as a possible etiology or co-factor. Closely related mouse strains, the N:NIH(S) and the CR:NIH(S), were examined for the hepatic abnormalities seen in the N:NIH(S)-B.